This invention relates to a swinging actuator for use in a magnetic disc type memory device, and more particularly a swinging actuator of the type wherein a carriage, that is a driving assembly including a magnetic head is inserted into gaps between stacked magnetic disc by a rotary motion so as to position the magnetic head mounted on the tip of the carriage at a predetermined position confronting respective discs by arcuately moving the magnetic head along the surfaces of the discs.
In recent years, efforts are concentrated to the improvement of the magnetic disc materials, and the improvement of the writing and reading device of the disc so as to provide a large capacity and high speed magnetic disc type memory device by storing informations at a high density and by reducing the access time.
As a result of constant improvement, at present a magnetic disc type memory device has been developed having a capacity of 3.2 giga bytes (8 disc units each having a capacity of 400 mega bytes are mounted) and an access performance of 20-30 times/giga byte/sec.
The term access performance is used herein, to mean the number of times of processing a unit information quantity per unit time. In a magnetic disc memory device the access performance usually tends to decrease as the memory capacity increases so that in order to increase the capacity and speed, the access performance should be improved. To solve this problem, it has been proposed to mount a plurality of magnetic heads on one arm of an actuator for narrowing the ranges of movements of respective magnetic heads for corresponding disc so as to reduce the access time or seek time.
According to this method, however, although the access time can be reduced by increasing the number of magnetic heads since the carriages carrying a plurality of magnetic heads constitute one actuator, there is a limit for the increase of the access performance.
Accordingly, it has also been proposed to divide a plurality of stacked magnetic discs into two groups, one actuator is provided for each group and the actuators are disposed at proper positions about the periphery of the discs. This type of the actuator is disclosed in Japanese laid open patent specification No. 44170 of 1981, for example.
In the actuator of this type a plurality of arms each supporting magnetic heads corresponding to respective magnetic discs are secured to one shaft, and the shaft, that is all arms are simultaneously rotated in accordance with an external control signal for moving respective magnetic head along the surfaces of corresponding magnetic discs. In this construction, however, since the respective actuators are disposed about the stack of the magnetic discs with a substantial spacing therebetween the size of the magnetic disc type memory device is considerably larger than that utilizing a single actuator.